Impulsive stimulated Raman effect is reviewed with a particular emphasis on the principles of the methodology. The key components are the force that the optical pulse exerts on the active mode, motion of the mode after the optical excitation, and the probing the time-evolution. In describing the excitation mechanism, we refer to electrostrictive force as a classical equivalence of the Raman effect. If integrated over the frequency, the intensity of the spontaneous Raman scattering is connected with the strength of the driving force. The motion of the mode following the optical impulse is interrogated with experimental configurations that read out the index change. The typical configurations are described from the viewpoint of optics. The grating method has a unique advantage for the study of the dispersion relation of propagating modes. The estimated degree of the index change is presented to show that the stimulated contribution builds up against the noise of the spontaneous Raman scattering.
